Statistics

Author

Chan, Kai Ler

Date of Issue

2017

School

School of Materials Science and Engineering

Abstract

The Vanadium Redox Flow Battery (VRFB) uses a single active element for both half-
cells, limiting cross contamination impacts while maintaining benefits of high energy
efficiency and large scale implementation via external energy storage. The VRFB consists
of vanadium electrolytes in two half-cells which undergo redox reactions to transfer
electrons across two electrodes as ions pass through the exchange membrane between the
half-cells to balance the charge. VRFB implements vanadium in both half-cells,
elimination cross-contamination problems. However, vanadium ion crossover is observed
for cation exchange membranes (CEM) such as Nafion, reducing cell capacity over time.
Coupled with high membrane costs, this encourages research into the alternative anion
exchange membranes (AEM), such as Fumatech membrane. Fumatech AEM bears
chemical stability and ion selectivity required for this application, though selectively
transferring hydroxyl anions instead of protons. Using UV-Visible Spectroscopy and
Energy Dispersive Spectroscopy (EDS), this AEM was found to adsorb significant
amounts of vanadium relative to the CEM, particularly V(V), likely contributing to high
resistivity and thus poor cell performance. Thermal sensitivity of the AEM is found to be
higher, making it unsuitable for high temperature applications. Electrolyte transfer was
also observed for the AEM. Vanadium crossover was reconfirmed in Nafion CEM, though
the impact on cell performance is still less significant compared to Fumatech AEM. An
overall comparison of cell parameters for both membranes shows Nafion CEM providing
greater practicality for VRFB application.